1. Field of the Invention
The invention relates generally to a movement converting mechanism involving a screwed rod and a gear part. More particularly, the invention provides a engaging head implemented in a movement converting mechanism to engage with a screwed rod.
2. Description of the Related Art
The use of a gear element engaging with a rotating screwed rod is well known in the art to produce convert a rotating movement to a translation movement. By further coupling the screwed rod with a step motor, the rotation angle of the screwed rod is accurately controlled, and an accurate translation and positioning of the moving unit to which is assembled the gear element is obtained. Therefore, this type of construction is common in movement mechanisms that require a highly accurate driving and positioning of the moving unit.
The disc reading/writing head of an optical disc drive is driven in motion by means of a similar mechanism as described above to read data on an optical disc. Conventionally, a wedge-shaped engaging head is fixedly attached to the disc reading/writing head. The engaging head has a gear part that engages with a screwed rod to drive the disc reading/writing head in translation. The construction of the engagement between the screwed rod and the engaging head is critical in order to obtain a highly accurate driving of the disc reading/writing head.
Conventionally, it is necessary to pre-load an engagement pressure in the engaging head so that when this latter is mounted and placed in a manner to mesh with the screwed rod, an adequate engagement pressure is produced between the screwed rod and the engaging head. This engagement pressure directly affects the accuracy of the movement converting mechanism: if the engagement pressure is too high, an excessive resistance hampers an effective driving from the step motor; if the engagement pressure is too small, a backlash may occur, which results in a driving error.
FIG. 1 is a schematic view illustrating an engaging head for a disc reading/writing head known in the art. As illustrated, the known engaging head comprises a main body 100 from which projects a supporting extension 106. A gear part 104 is connected to the supporting extension 106 via a connecting portion 102. The connecting portion 102 is relatively thinner, which creates a certain flexibility that enables a deflection of the gear part 104 relative to the main body 100 to engage with the screwed rod. To pre-load an engagement pressure in the engaging head, a spring 108 has an end fixedly attached to the main body 100, and an opposite end abutted against an inner surface of the gear part 104.
To obtain pre-load a desired engagement pressure, the inclination of the spring 108 and its contact point with the inner surface of the gear part 104 have to be controlled, and the positioning of the spring 108 further has to be accurately controlled. This construction is not satisfactory because it results in an inconstant yield.
An aspect of the invention is therefore to provide an engaging head that, implemented in a movement converting mechanism to engage with a screwed rod, and more particularly in a movement converting mechanism for an optical disc drive, allows an effective control of the pre-loaded engagement pressure with the screwed rod.
Another aspect of the invention is to provide an engaging head used in a movement converting mechanism that provides a good yield.
Furthermore, another aspect of the invention is to provide an engaging head that simplifies the construction of the movement converting mechanism.
To accomplish the above and other objectives, an engaging head of the invention, implemented in a movement converting mechanism to engage with a screwed rod, comprises an attachment body, a gear part, and a resilient pre-loading element. The attachment body has a pushing sidewall. The gear part has an inner surface facing the pushing sidewall of the attachment body, and an opposite outer surface provided with gear teeth. The resilient pre-loading element is made of specifically adequate materials that are, according to the invention, silicon sponges, rubber, plastics, or foam sponges. The resilient pre-loading element is mounted between the pushing sidewall of the attachment body and the inner surface, and has a side abutting against the pushing sidewall and another side abutting against the inner surface of the gear part. Being compressed between the pushing sidewall and the inner surface, the resilient pre-loading element thereby exerts a pre-loaded engagement pressure that results in a deflection of the gear part to ensure an adequate engagement of the gear teeth with the screwed rod.
According to an embodiment of the invention, the resilient pre-loading element is directly attached to the pushing sidewall of the attachment body and the inner surface of the gear part.
According to a variant embodiment of the invention, the gear part is further connected to the pushing sidewall of the attachment body via a supporting extension that projects from the pushing sidewall of the attachment body. A connecting portion connects the gear part to the supporting extension, and is sufficiently flexible to allow a deflection of the gear part. The pushing sidewall of the attachment body, the supporting extension, and the inner surface of the gear part thereby define an accommodating space in which is mounted the resilient pre-loading element by insertion. Optionally, the supporting extension further sideways forms two reinforcement flanks, and a cover projects from the pushing sidewall of the attachment body over the accommodating space to confine the resilient pre-loading element therein.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.